The present invention relates generally to systems for controllably disabling cylinders in an internal combustion engine, and more specifically to such systems operable to do so by controlling air intake, fueling and spark timing.
Systems for disabling one or more cylinders in an internal combustion engine are known. Such systems are typically operable to disable one or more cylinders in an effort to improve fuel economy under certain engine operating conditions; e.g., steady state and engine idling conditions. However, such known cylinder disabling systems have a number of drawbacks associated therewith.
For example, in engines having mechanically or electronically controlled intake air throttles, engine operation under partial throttle, cruise control and idle control are typically over-throttled, thereby resulting in unnecessary fuel loss. While disabling cylinders; i.e., by selectively disabling operation of one or more cylinders via corresponding cylinder valve deactivation devices or by disabling fueling to one or more cylinders, is known to reduce such throttle losses, the resulting accelerator pedal position required to maintain a engine output torque at a given engine rotational speed becomes xe2x80x9cdeeperxe2x80x9d with each cylinder that is disabled. As a specific example, if cruising at 35 mph requires 25% accelerator pedal deflection with all cylinders enabled, 75% accelerator pedal deflection may be required if some of the cylinders are disabled. Moreover, cylinder disabling under engine idle conditions using known techniques tends to result in undesirable engine/vehicle vibration.
As another example, it is widely recognized that modulating engine output power around xe2x80x9cdeceleration fuel cut offxe2x80x9d (DFCO), or zero indicated engine output torque, is difficult to accomplish. This is largely due to a non-linear relationship that exists between engine output torque increase/decrease and cylinder enabling/disabling. While known DFCO control strategies provide for some improvement, they are generally understood to be inaccurate due to such non-linearities. Additionally, known DFCO control strategies generate high vacuum conditions in the intake manifold, and the fuel consequently does not completely burn in the combustion chambers due to a lack of oxygen. This incomplete combustion generates undesirable increases in hydrocarbon (HC) carbon dioxide (CO) emissions produced by the engine.
What is therefore needed is an improved system for controllably disabling cylinders in an internal combustion engine that does not suffer from the drawbacks of known cylinder disabling strategies.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a method is provided comprising the steps of computing a minimum number of a total number of cylinders required to achieve a desired engine/vehicle operating parameter value, computing a maximum throttle position of a throttle controlling air flow into an intake manifold of the engine, enabling operation of the minimum number of cylinders while disabling operation of remaining ones of the total number of cylinders, opening the air intake throttle to the maximum throttle position, determining a current value of the engine/vehicle operating parameter, and controlling ignition timing sufficiently to drive the current value of the engine/vehicle operating parameter to the desired engine/vehicle operating parameter value.
In accordance with another aspect of the present invention, a method is provided comprising the steps of determining air pressure within an intake manifold of the engine, determining rotational speed of the engine, determining road speed of a vehicle carrying the engine, and disabling operation of a number of cylinders of the engine while maintaining an engine/vehicle operating parameter near a desired value of the engine/vehicle operating parameter if the air pressure is below a pressure threshold, the rotational speed of the engine is greater than an engine speed threshold and the road speed of the vehicle is greater than a vehicle speed threshold.
In accordance with a further aspect of the present invention, a method is provided comprising the steps of determining air pressure within an intake manifold of the engine and disabling operation of a number of cylinders of the engine while maintaining a current value of an engine/vehicle operating parameter near a desired value of the engine/vehicle operating parameter if the air pressure is below a first pressure threshold and one of the desired value of the engine/vehicle operating parameter is below an operating parameter threshold and the air pressure is below a second pressure threshold.
The present invention provides a system for controllably disabling cylinders in an internal combustion engine via control of engine fueling or a number of cylinder valve disabling devices, intake manifold throttle position and ignition timing.
The present invention provides such a system for disabling one or more cylinders to improve fuel economy while maintaining an engine/vehicle operating parameter near a desired engine/vehicle operating parameter value.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.